From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 0C25D6B0047 for ; Sat, 4 Sep 2010 22:51:20 -0400 (EDT) Received: by iwn33 with SMTP id 33so3935551iwn.14 for ; Sat, 04 Sep 2010 19:51:19 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20100904020452.GA7788@localhost> References: <1283438087-11842-1-git-send-email-minchan.kim@gmail.com> <20100903170227.b2f18ba4.akpm@linux-foundation.org> <20100904020452.GA7788@localhost> Date: Sun, 5 Sep 2010 11:51:19 +0900 Message-ID: Subject: Re: [RESEND PATCH v2] compaction: fix COMPACTPAGEFAILED counting From: Minchan Kim Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Wu Fengguang Cc: Andrew Morton , Christoph Lameter , Hugh Dickins , Andi Kleen , Mel Gorman , linux-mm , LKML List-ID: On Sat, Sep 4, 2010 at 11:04 AM, Wu Fengguang wrot= e: > On Sat, Sep 04, 2010 at 08:02:27AM +0800, Andrew Morton wrote: >> On Thu, =A02 Sep 2010 23:34:47 +0900 >> Minchan Kim wrote: >> >> > Now update_nr_listpages doesn't have a role. That's because >> > lists passed is always empty just after calling migrate_pages. >> > The migrate_pages cleans up page list which have failed to migrate >> > before returning by aaa994b3. >> > >> > =A0[PATCH] page migration: handle freeing of pages in migrate_pages() >> > >> > =A0Do not leave pages on the lists passed to migrate_pages(). =A0Seems= that we will >> > =A0not need any postprocessing of pages. =A0This will simplify the han= dling of >> > =A0pages by the callers of migrate_pages(). >> > >> > At that time, we thought we don't need any postprocessing of pages. >> > But the situation is changed. The compaction need to know the number o= f >> > failed to migrate for COMPACTPAGEFAILED stat >> > >> > This patch makes new rule for caller of migrate_pages to call putback_= lru_pages. >> > So caller need to clean up the lists so it has a chance to postprocess= the pages. >> > [suggested by Christoph Lameter] >> >> I'm having trouble predicting what the user-visible effects of this bug >> might be. =A0Just an inaccuracy in the COMPACTPAGEFAILED vm event? > > Right, it's an accounting fix. Before patch COMPACTPAGEFAILED will > remain 0 regardless of how many migration failures. > > The patch does slightly add dependency for migrate_pages() to return > error code properly. Before patch, migrate_pages() calls > putback_lru_pages() regardless of the error code. After patch, the > migrate_pages() callers will check its return value before calling > putback_lru_pages(). > > In current code, the two conditions do seem to match: > > "some pages remained in the *from list" =3D=3D "migrate_pages() returns a= n error code". Exactly. Thanks for the answering instead of me, Wu. :) > Thanks, > Fengguang > --=20 Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org